Micro-Structure and Fracture Behavior of High-Melt-Strength PPs Prepared by Reactive Extrusion

Abstract

In this study, high-melt-strength polypropylenes (PPs) were prepared by reactive extrusion of PP and varied amount of divinylbenzene in the presence of dicumyl peroxide and an antioxidant, and the dynamic rheological behavior, crystalline morphology, and fracture behavior of the resultant materials were investigated. It was found that at relatively low frequency, with the cross-linking and branching structures increasing, the complex viscosity of the melt of the modified PP increased significantly and then leveled off. The modulus of the melt, particularly the storage modulus, increased. The storage moduli of the melts with higher content of cross-linking and branching structures were higher than the loss modulus in the whole range of testing frequency, indicative of a completely elastic behavior. The crystallinity and the size of spherulites of the modified PP decreased, while the number of spherulites increased. The specific essential work of fracture and the specific non-essential work of fracture of the modified PP were found to be reduced compared with pure PP, but the specific essential work of fracture showed an increasing trend with the cross-linking and branching structures increasing.

Keywords:

• branching
• cross-linking
• crystallization
• essential work of fracture
• high melt strength
• polypropylene
• rheological behavior

Acknowledgments

The authors gratefully acknowledge the financial support of this work by the National Natural Science Foundation of China (grants numbers 50873068 and 50673066).